1. Field of the Invention
This invention relates to a photoelectric transducer.
2. Prior Art Statement
There has been a number of approaches to increasing the efficiency of photoelectric transducers. One way of providing an overall improvement in the conversion efficiency of the transducer by mechanical or physical structural adaptations is a method employed for crystalline silicon solar cells. In this method, one of the upper and lower surfaces of the p-n junction or other such planar semiconductor structure which forms the transduction element where the photoelectric conversion takes place is textured. Anisotropic etching of crystalline surface is employed to form clusters of pyramid-shaped or wave-shaped projections directly on the said surface.
In the absence of such surface texturing, light impinging perpendicularly onto the transducer will pass through the planar transduction element portion by the shortest route, in the thickness direction. However, if the propagation of the light is at an angle, in effect the length of the light path through the planar transduction element portion will be increased, enabling more of the incident light, and light reflected from the surface on the opposite side to the incident light surface, to be utilized in the photoelectric conversion process.
However, the method whereby the texturing is formed directly on the surface of the planar transduction element portion by etching is only effective with crystal systems having anisotropic etching characteristics, and even then only on a (100) plane, is not applicable to surfaces that do not have such anisotropic etching characteristics, such as polycrystals with no specific crystal plane index, or to a crystal system with a (111) plane. In addition, in optical terms an improvement in conversion efficiency usually can be expected, but because the surface with the pyramid-shaped or wave-shaped texture elements thus formed by anisotropic etching has a high carrier recombination velocity, electrically there is an increase in the conversion loss. The overall result has therefore been an insufficient improvement effect.